The present invention relates to video coding techniques.
Video distribution systems include a video source and at least one receiving device. The video content may be distributed over a network, such as broadcast television, Over The Top (OTT) delivery, Internet Protocol Television (IPTV), etc., or over fixed media, such as Blu-ray, DVDs, etc. To keep complexity and cost low, video content is typically limited in dynamic range, e.g., 8-10 bit signal representations and 4:2:0 color format.
Recent advances in display technology, however, have opened the door for the use of more sophisticated content, including content characterized as High Dynamic Range (HDR) and/or wide color gamut (WCG), as well as content with increased spatial and/or temporal resolution. High Dynamic Range content are essentially characterized by an increased dynamic range, which is described as the ratio between the largest and smallest possible values that are represented in the signal. For video content, in particular, there is an interest in supporting content that can have values as small as 0.005 nits (cd/m2), where the nit unit is a metric used to measure/specify luminance, up to 10000 nits in the entertainment space, whereas in other academic and scientific spaces lower and higher values are also of interest. Wide color gamut content, on the other hand, is content that is characterized by a larger representation of color information than is currently common in the industry, which is rather limited. In some applications it is even desirable to be able to represent the color gamut space that humans can perceive. These features can help in providing a more “lifelike” experience to the viewer.
Also, content providers are given more “artistic” flexibility because of the increased choices. This higher quality content is typically converted to a lower range using a Transfer Function (TF) and color conversion before encoding for distribution using a video codec system. These steps can introduce banding and other artifacts that may impact and substantially degrade the quality of the video content when decoded and displayed. In particular, the conversion (initial quantization) stemming from the TF and color conversion can introduce a first error, Eq, which is carried through the entire process, and the encoding can introduce an additional error, Ee. Further, errors (e.g., Eq) can be compounded because conventional encoders make similarity/distortion measures that are based on the “in process” video source, i.e., the converted signal.
Therefore, the inventors perceived a need in the art for an improved encoding process capable of handling higher quality content that results in an improved experience at the decoder compared to conventional encoders, and may reduce banding, improve resolution, as well as reduce other artifacts.